On Wed, 2013-10-02 at 12:48 +0200, Alexander Gordeev wrote:

This series is against "next" branch in Bjorn's repo:
git://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci.git

Currently pci_enable_msi_block() and pci_enable_msix() interfaces
return a error code in case of failure, 0 in case of success and a
positive value which indicates the number of MSI-X/MSI interrupts
that could have been allocated. The latter value should be passed
to a repeated call to the interfaces until a failure or success:


	for (i = 0; i < FOO_DRIVER_MAXIMUM_NVEC; i++)
		adapter->msix_entries[i].entry = i;

	while (nvec >= FOO_DRIVER_MINIMUM_NVEC) {
		rc = pci_enable_msix(adapter->pdev,
				     adapter->msix_entries, nvec);
		if (rc > 0)
			nvec = rc;
		else
			return rc;
	}

	return -ENOSPC;


This technique proved to be confusing and error-prone. Vast share
of device drivers simply fail to follow the described guidelines.

This update converts pci_enable_msix() and pci_enable_msi_block()
interfaces to canonical kernel functions and makes them return a
error code in case of failure or 0 in case of success.

[...]

I think this is fundamentally flawed: pci_msix_table_size() and
pci_get_msi_cap() can only report the limits of the *device* (which the
driver usually already knows), whereas MSI allocation can also be
constrained due to *global* limits on the number of distinct IRQs.

Currently pci_enable_msix() will report a positive value if it fails due
to the global limit.  Your patch 7 removes that.  pci_enable_msi_block()
unfortunately doesn't appear to do this.

It seems to me that a more useful interface would take a minimum and
maximum number of vectors from the driver.  This wouldn't allow the
driver to specify that it could only accept, say, any even number within
a certain range, but you could still leave the current functions
available for any driver that needs that.

Ben.

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